The speed that aerodynamics are important

[aerohead]

A friend of my dad was a sprint car racer and speed shop owner in Long Beach, CA.
If a potential customer asked, ' How fast can you make my car go? ' his reply was always, ' How much money do you have ?'

[bwilson4web]

With an efficient car like a Prius or M3 Tesla, I use 45 mph as the transition speed. It is not a single dimension speed.

Bob Wilson

[Piotrsko]

Not a bad point. Most small aircraft generally stall at that speed so there might be some correlation

[awy]

"significant" has a more concrete meaning when understood as part of an optimization problem together with rolling resistance etc tradeoff considerations. op's statement can be transformed into "speed at which aero becomes significant factor in vehicle design."

take a bicycle for instance, there's often tradeoff between rolling resistance/weight and aero. it's why climbing bikes have a different design compared to time trialing bikes. significance is understood as relative to other design considerations.

[mpg_numbers_guy]

Aero has significant impact. I notice this daily when comparing my old G1 Insight to my current Prius C.

The Prius C gets the same (if not better) fuel economy around town (probably due to the bypassed IMA on the Insight) but on the highway the Insight got a full 10+ mpg better. The Insight is aerodynamically shaped with a 0.25 cD while the Prius C has a worse 0.28 and doesn't coast as well despite weighing ~700lbs more. My wife's old Volvo S60 also has a cD of 0.28 but coasted just as well as the Insight, but the Volvo weighed almost twice what the Insight did so there was more kinetic energy available while coasting.

[Phase]

I just always say 45-50 is the magic aero number of when it matters. Sure you can measure above 35 mph like for tuft testing and stuff, but a lot of tests show that 45 is when rolling resistance and aero are the same load. So 45 for an average car, and 50 mph for a more aero car. If I’m hypermiling to the super max, I try to stay around 50. Sure 45 may give a few extra mpg, but it’s diminishing returns

[Isaac Zachary]

As cars have become heavier, more aerodynamic and come with more powerful engines, the result is that the speed at which you get the best fuel mileage has risen.

It used to be around 30mph in many cars (looking at a graph from Glenn's Gas Guzzlers Guide from 1975). In my Hybrid Avalon it's closer to 55mph.

The thing is there is a transition from where the engine is more inefficient from being under too low of a load to where the aerodynamic drag is the major factor in fuel mileage.

[aerohead]

https://ecomodder.com/forum/member-a...sugar-cube.jpghttps://ecomodder.com/forum/member-a...oads-up-18.jpghere are some numbers I pencil-whipped for the Chevy BOLT I'll be getting in September.
I used Cd 0.31, Af 25.7-sq-ft, 0.00238 slugs air density, and 3,880-lb test weight.
Aerodynamic horsepower requirements are presented in 5-mph increments, from zero-to 100-mph:
0-mph = 0
5-mph = 0.0067
10-mph = 0.054
15-mph = 0.183
20-mph = 0.435
25-mph = 0.8497
30-mph = 1.4683
35-mph = 2.3316
40-mph = 3.4805
45-mph = 4.9557
50-mph = 6.7979
55-mph = 9.048
60-mph = 11.7468
65-mph = 14.9351
70-mph = 18.6535
75-mph = 22.943
80-mph = 27.8444
85-mph = 33.3983
90-mph = 39.6456
95-mph = 46.6371
100-mph = 54.3836
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Over the same speed spread, power absorbed from rolling-resistance increased linearly, from zero, to 8.9873-hp ( using a Cfrr of 0.008686291 ( probably 'high' )) [ Bridgestone Ecopia is around 0.005 ].
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If everyone constructs one of these tables from 'day one', 'curves' can be constructed from the data-plots for aero and R-R, plus adjustment for mechanical efficiency, and presuming a constant BSFC, or BSFC-e for BEVs, one can predict, at any chosen velocity, what mpg, or 'range' their vehicle will return.
I photo-reduced my table and chart, in full color, at a local UPS/ Post Office store, and laminated it, creating a 'card' which fits in my fanny pack or clipboard, for 'thinking' and trip-planning.
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PS:
Because I ran these numbers, I know from the science that with aero mods, the BOLT has a shot at over 300-miles range on it's 'recall' 63-kWh pack, before I've bought it.
'Knowledge is Power'
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Extra PS:
here's a very old, pre-radial tire power graph for rolling-resistance vs velocity. It's 'nothing' compared to aerodynamics
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extra extra PS
Here's the aerodynamic challenge. The hen egg and sugar cube have identical drag ( Thanks to Chrysler Corporation for the data ).
The hen egg is 21-X larger than the sugar cube, yet 'same' drag.

[Isaac Zachary]

Originally Posted by aerohead

here are some numbers I pencil-whipped for the Chevy BOLT I'll be getting in September.
I used Cd 0.31, Af 25.7-sq-ft, 0.00238 slugs air density, and 3,880-lb test weight.
Aerodynamic horsepower requirements are presented in 5-mph increments, from zero-to 100-mph:
0-mph = 0
5-mph = 0.0067
10-mph = 0.054
15-mph = 0.183
20-mph = 0.435
25-mph = 0.8497
30-mph = 1.4683
35-mph = 2.3316
40-mph = 3.4805
45-mph = 4.9557
50-mph = 6.7979
55-mph = 9.048
60-mph = 11.7468
65-mph = 14.9351
70-mph = 18.6535
75-mph = 22.943
80-mph = 27.8444
85-mph = 33.3983
90-mph = 39.6456
95-mph = 46.6371
100-mph = 54.3836
-------------------------------------------------------------------------------------
Over the same speed spread, power absorbed from rolling-resistance increased linearly, from zero, to 8.9873-hp ( using a Cfrr of 0.008686291 ( probably 'high' )) [ Bridgestone Ecopia is around 0.005 ].
--------------------------------------------------------------------------------------
If everyone constructs one of these tables from 'day one', 'curves' can be constructed from the data-plots for aero and R-R, plus adjustment for mechanical efficiency, and presuming a constant BSFC, or BSFC-e for BEVs, one can predict, at any chosen velocity, what mpg, or 'range' their vehicle will return.

With EV's the speed has a greater effect on range since the efficiency of the motor doesn't go down so much at lower speeds.

I remember when I had the Nissan Leaf that someone had done the work to figure out what speed would give the Leaf the greatest range, and it was 12mph.

I would sometimes start a long trip creeping along at 25mph which would give me quite a range advantage, sometimes getting over 100 miles with juice to spare in an EV that had an advertised range of 71 miles at that point.

[aerohead]

Yes. This phenomena is clearly supported by fact.
With the 'thermal' efficiency of a BEV power-electronics and motor, we end up with the 2nd-Law of Thermodynamics equivalency of an 'ADIABATIC engine', almost 100%.
On paper, and considering rolling-resistance, a 50% drag reduction on the BOLT will yield a 51.1% range improvement at 65-mph, which is what I'll drive at.
AeroStealth tested his 2014 Ford F-150 4X4, 6'-bed EcoBoost for 'speed.'
At 35-mph he gets 32-mpg in the 5,800-lb curb weight pickup, compared to 21-mpg on it's best day on the Interstate.
The velocity-cubed relationship between velocity and power is a real butt-kicker!